W3cubDocs

/C++

std::basic_string<CharT,Traits,Allocator>::size, std::basic_string<CharT,Traits,Allocator>::length

	(1)
size_type size() const;		(until C++11)
size_type size() const noexcept;		(since C++11) (until C++20)
constexpr size_type size() const noexcept;		(since C++20)
	(2)
size_type length() const;		(until C++11)
size_type length() const noexcept;		(since C++11) (until C++20)
constexpr size_type length() const noexcept;		(since C++20)

Returns the number of CharT elements in the string, i.e. std::distance(begin(), end()).

Parameters

(none).

Return value

The number of CharT elements in the string.

Complexity

Unspecified.	(until C++11)
Constant.	(since C++11)

Notes

For std::string, the elements are bytes (objects of type char), which are not the same as characters if a multibyte encoding such as UTF-8 is used.

Example

#include <cassert>
#include <iterator>
#include <string>
 
int main()
{
    std::string s("Exemplar");
    assert(8 == s.size());
    assert(s.size() == s.length());
    assert(s.size() == static_cast<std::string::size_type>(
        std::distance(s.begin(), s.end())));
 
    std::u32string a(U"ハロー・ワールド"); // 8 code points
    assert(8 == a.size()); // 8 code units in UTF-32
 
    std::u16string b(u"ハロー・ワールド"); // 8 code points
    assert(8 == b.size()); // 8 code units in UTF-16
 
    std::string c("ハロー・ワールド"); // 8 code points
    assert(24 == c.size()); // 24 code units in UTF-8
 
    #if __cplusplus >= 202002
    std::u8string d(u8"ハロー・ワールド"); // 8 code points
    assert(24 == d.size()); // 24 code units in UTF-8
    #endif
}